Magnetically active materials are used for many applications in the electronics industry. Layers of magnetically active material are incorporated into disks used for hard disk drives and into magnetic (or magnetoresistive) random access memory (MRAMs) chips. Each of these applications requires a layer of magnetic material to be formed on a substrate and then patterned with domains that can be separately magnetized or demagnetized.
The disk in a hard-disk drive is configured with magnetic domains that are separately addressable by a magnetic head. The magnetic head moves into proximity with a magnetic domain and alters the magnetic properties of the domain to record information. To recover the recorded information, the magnetic head moves into proximity with the domain and detects the magnetic properties of the domain. The magnetic properties of the domain are generally interpreted as corresponding to one of two possible states, the “0” state and the “1” state. In this way, digital information may be recorded on the magnetic medium and recovered thereafter.
The magnetic medium in a hard-disk drive is generally a glass, composite glass/ceramic, or metal substrate, which is generally non-magnetic, with a magnetically susceptible material deposited thereon. The magnetically susceptible layer is generally deposited to form a pattern, such that the surface of the disk has areas of magnetic susceptibility interspersed with areas of magnetic inactivity. The non-magnetic substrate is usually topographically patterned, and the magnetically susceptible material deposited by spin-coating or electroplating. The disk may then be polished or planarized to expose the non-magnetic boundaries around the magnetic domains. In some cases, the magnetic material is deposited in a patterned way to form magnetic grains or dots separated by a non-magnetic area.
Such methods are expected to yield storage structures capable of supporting data density up to about 1 TB/in2, with individual domains having dimensions as small as 20 nm. Where domains with different spin orientations meet, there is a region referred to as a Bloch wall in which the spin orientation goes through a transition from the first orientation to the second. The width of this transition region limits the areal density of information storage because the Bloch wall occupies an increasing portion of the total magnetic domain.
To overcome the limit due to Bloch wall width in continuous magnetic thin films, the domains can be physically separated by a non-magnetic region, which can be narrower than the width of a Bloch wall in a continuous magnetic thin film. Conventional approaches to creating discrete magnetic and non-magnetic areas on a medium have focused on forming single bit magnetic domains that are completely separate from each other, either by depositing the magnetic domains as separate islands or by removing material from a continuous magnetic film to physically separate the magnetic domains. In some processes, a substrate is masked and patterned, and a magnetic material deposited over unmasked portions of the substrate. In other processes, magnetic material is deposited on a substrate before masking and patterning, and is then etched away in exposed portions. In either case, the topography of the substrate is altered by deposition or etching of the residual pattern of the magnetic regions. Because the read-write head of a typical hard-disk drive may fly as close as 2 nm from the surface of the disk, these topographic alterations can become limiting. Thus, there is a need for a process or method of patterning magnetic media that has high resolution and does not alter the topography of the media, and an apparatus for performing the process or method efficiently for high volume manufacturing.